In its broadest sense, the present invention addresses impact absorption of a moving human body against a resisting surface. More specifically, and as related to the environment of bedding products to which the described embodiments of the invention find illustration, the movement of a body against a cushioning and supporting surface is in point.
In general terms, an impact absorbing device should arrest a moving body with minimum stress of the body and the device. One may characterize the absorption of kinetic energy in the device such that an equivalent amount may be utilized elsewhere (such as reinstating this kinetic energy back to the body at some time after impact) as an elastic impact. Alternatively an inelastic impact between the body and the device may occur, such that effectively all of the kinetic energy is dissipated by the device upon impact.
Inelastic collisions may commonly be found in many safety devices such as air bags, automobile interior panels, and crash helmets. Such devices, although effectively operating for their intended purpose, often may be used only once due to the severity of impact and the materials of construction.
Between the extremes of inelastic and elastic impacts are structures providing elastic impacts damped by some means. Structure using such damping effects may rely upon the material of the structure, structural component interactions, or the environment in which the structure is located, or some combination thereof.
In the bedding products area in which this invention finds its origin, mattress innerspring units are generally formed of a conventional plurality of spring coils arranged in side-by-side relation in parallel rows, with parallel columns also thereby being formed orthogonal to the rows. Border wires typically encircle both the upper and lower perimeters, which for purposes of further discussion, will be referred to as top and bottom perimeters respectively. Box spring foundations are also generally formed of a combination of helical or torsion springs supported by a base defined by wood side rails and end rails, with wood or steel spans extending between either the side or end rails. A wire grid or the like is typically used to form the top or support surface of the foundation. The helical or torsional springs used in the innerspring or foundation perform the impact absorption, and then support functions described.
Besides fundamental impact absorption and support, another consideration in bedding product design and manufacture is the ability to make units with different firmness characteristics suited to ranges of consumer preference. This is typically accomplished by providing several product lines having different firmness, achieved by using springs of different spring constant or by adding/removing springs; in even more sophisticated bedding products, providing areas of differing firmness in a given bedding product by mixing spring kind or count.
As may be readily recognized, producing springs of differing spring constants, ordinarily achieved by making the various springs out of different wire stock or in different configurations, results in a multiplicity of spring manufacturing processes and the necessity of stocking the different springs. While the overall layout, configuration or count may also be changed for each product firmness, this again increases the number of assembly jigs required, or at a minimum increases the complexity of product assembly.
Use of heavier wire stock, different spring fabrication machinery, more springs, or different layouts obviously adds expense to bedding product construction in terms of material and labor. A significant consideration in making bedding products with different firmness characteristics is therefore to do so in the most efficient and economical manner.
Non-wire spring bedding structures have been disclosed. One example is shown in U.S. Pat. No. 3,242,512, which discloses a resilient load supporting device consisting of a vented bellows spring cushioning assembly. In this reference, each bellows spring component is manufactured from a polymeric resilient and flexible material of rubber or the equivalent. Each such "spring" is formed not unlike the bellows of an accordion, but with a circular cross-section. The thickness of the bellows varies.
Each spring of the '512 structure functions to resist a load by collapsing along a wall circumference that is the least in thickness until fully collapsed, and then a slightly thicker wall section will collapse in a similar manner until the spring is fully collapsed. Moreover, the springs may be interleaved such that the spring ribs are in substantial contact with a neighboring spring, thereby providing additional resistance to the collapse of an individually loaded spring. Friction between ribs of the interleaved springs during loading provides a second force counteracting the compression of a loaded spring. This friction also allows for further compression of each individual rib, which reacts accordingly by expanding radially and contracting axially thereby providing a third force grounded on the compressive characteristics of the material used in spring construction. Each of the hollow springs is freely vented to the atmosphere to allow the spring to readily vent the air within the interior of the spring upon compression as well as to refill the interior of the spring upon release of a force from an impacting body. Each spring is attached to a rubber pad stretched onto the base of a load supporting structure.
Similarly, in U.S. Pat. No. 3,262,138 a vented bellows assembly is disclosed. Again, the rib bellows structures are interleaved among themselves and have venting sufficient to provide pneumatic resistance to cooperate with the control cushioning effect obtained by the interactive flexing of the bellows ribs. The springs may be secured to a load supporting structure by means of caps at either or both ends of the spring which extend through the structures.
Alternatively, an entire structure may be altered to create damping effects sufficient for a given use. Such structure is disclosed in U.S. Pat. No. 3,251,076. In this patent, an impact cushioning mat structure is disclosed with an interior modified to define individual air cells interconnected in a hexagonal or square configuration. The passage of air between cells provides an inelastic component to the elastic behavior of the material comprising the mat structure. In essence, the retained kinetic energy in the structure is just sufficient to restore the mats to their original state after an impact, thereby effectively eliminating the possibility of a rebound of the impacting body. The disclosed structure resists a load by deforming a cavity in the area of the load which dispels air to adjoining cavities via orifices or the like. The combination of the air pressure within the cavity and cavity structure consequently resist the applied load and absorb the kinetic energy of the load.
Given the state of this art, it can be seen that it would be desirable to have impact absorbing and supporting devices that have non-uniform elastic propensities, such that load supporting structures composed of individual devices may have a gradient of "spring constants" over a given area of the structure. It would also be desirable to have a single spring construction that can be readily altered to change its spring characteristics.
Moreover, there is a further need in the art for such impact absorbing devices that provide for easy installation on bases and frames of conventional load supporting structures in the bedding products industry. In this vein, it is of note that the foregoing discussion of the non-conventional spring references include structures of an unconventional composition that require altogether unconventional base supports and coverings. Efforts to develop attachment elements for both the top and bottom (i.e., the ends) of a spring which simplify assembly of the springs into the mattress, foundation, cushion, etc., are ongoing in the bedding and furniture industries.
It is therefore an objective of this invention to provide a load supporting structure which utilizes pneumatic springs, is relatively simple in construction, economical to fabricate, readily adjustable in spring characteristic, easy to assemble and install, and otherwise ideally suited to its intended purposes as a cushioning element.